The present invention relates to a cutting tool employing indexable cutting inserts and in particular a milling cutter retaining round cutting inserts.
Cutting tools having cutting inserts with round cutting edges are known. Typically, a cutting insert of this kind comprises a round upper surface, a round lower surface and a side surface extending between the upper and lower surfaces. The intersection of the upper surface and the side surface forms a round cutting edge. An example of a cutting insert of such a kind is disclosed in U.S. Pat. No. 5,934,844 to Woolley. Typically, the cutting insert is retained in an insert receiving pocket formed in a forward portion of the tool.
A simple way of retaining the cutting insert to the insert receiving pocket is by using a retaining screw that passes through a through bore in the cutting insert and threadingly engages a threaded bore in a base wall of the insert receiving pocket. A disadvantage of this kind of cutting tool is that the cutting insert may rotate about its axis during machining. Also, radial and axial cutting forces acting on the cutting insert which is supported only by the retaining screw, a fact that limits the use of such a cutting tool to light machining conditions.
There are known cutting tools that provide support to the side of the insert. For example, U.S. Pat. No. 5,346,336 to Roscigno discloses a metal cutting insert that comprises a top surface which is intersected by a frusto-conical edge surface to form therewith a round cutting edge. Five equidistantly spaced flat facets are formed in the edge surface. Upper ends of the facets are spaced below the cutting edge. A fixing screw secures the insert to the seat of a holder, such that two of the facets are pressed against respective flat contact areas formed on a locating surface of the holder. Each facet forms an acute angle relative to a central axis of the insert.
A disadvantage of the insert and holder of ""336 is that the number of indexing positions is limited and it depends on the required angle between the two flat contact areas of the holder. Furthermore, the insert is not provided with supporting means to prevent loading and bending of the fixing screw as a result of radially outwardly directed forces that act, for example, in the direction of the arrow of the numeral 10 in FIG. 4 of ""336.
Other cutting inserts having flat support surfaces on their side surfaces are shown, for example, in U.S. Pat. No. 6,053,671 to Stedt et al., U.S. Pat. No. 6,152,658 to Satran et al. and U.S. Pat. No. 6,164,878 to Satran et al. In these patents, a lower surface of the insert abuts a base wall of the insert receiving pocket and the side surface of the insert is pressed against a side wall of the insert receiving pocket. In order to index each of these cutting inserts into a new cutting position, the retaining screw has to be completely loosened and the cutting insert has to be lifted upwardly from its pocket until its side abutment surfaces no longer abut the side walls of the insert receiving pocket. Only then, the insert can be rotated into a new indexed position.
In U.S. Pat. No. 5,658,100 to Deiss et al. there is disclosed a cutting insert in which its lower surface abuts a base wall of the insert receiving pocket. The insert is secured to the base wall by means of a retaining screw. In order to prevent rotation of the cutting insert about its axis, the cutting insert is provided with a plurality of depressions in its top surface. The depressions are engaged by a clamping claw that is supported on the tool body and retained thereto by means of a securing screw.
The clamping claw of ""100 complicates the construction of the tool and may disturb the flow of chips during machining. Furthermore, a disadvantage of the tool of ""100 is that it is necessary to loosen both the securing screw of the clamping claw and the retaining screw of the cutting insert in order to enable rotation of the insert into another indexing position. During the rotation of the cutting insert into a new indexing position attention must be given to the exact rotational position of the cutting insert in order to guarantee that the desired depression is opposite the clamping claw to enable their mutual engagement.
In U.S. Pat. No. 5,236,288 to Flueckiger there is disclosed a round indexable cutting insert in which its lower surface abuts a base wall of an insert receiving pocket. The cutting insert is retained in the pocket by means of a retaining screw. The cutting insert is locked in fixed angular position in the pocket by a conically tipped screw which seats in a recess formed in the back face of the insert.
A disadvantage of the cutter of ""288 is that the cutting insert is not well supported against radially outwardly directed cutting forces that tend to withdraw the cutting insert from its pocket. Furthermore, in order to rotate the cutting insert to a next indexing position it is required to loosen both the retaining screw and the conically tipped screw.
Another example for fastening round cutting inserts to their pockets is shown in U.S. Pat. No. 5,810,518 to Wiman et al. As shown in FIG. 5 of ""518, a cutting insert is mounted on a support surface of an insert holder. The insert includes a bottom surface having grooves and planar surface portions disposed between the grooves. The support surface includes ribs which fit into respective grooves of the insert. Some of the planar surface portions of the insert bear against a planar, rib-free portion of the support surface.
Despite the fact that the ribs-grooves arrangement prevents rotation of the cutting insert, this arrangement significantly reduces the total area of the mutual tangential, axial and radial abutment surfaces between the cutting insert and its holder and, therefore, such an arrangement is not adequate for heavy machining conditions since it depends on the load carrying capacity of the retaining screw that retains the cutting insert to its holder.
In U.S. Pat. No. 4,812,087 to Stashko there is disclosed an end milling cutter that retains a plurality of round cutting inserts. Each of the inserts is mounted in an insert seat having, according to one embodiment, at least one pair of flat side surfaces in abutting relationship with associated surfaces in the pocket to obtain maximum rigidity in seating and prevent rotation of the insert. According to another embodiment, each insert seat is a rearwardly extending recess having its rear wall comprising a frusto-conical portion terminating in a lower cylindrical portion. The cutting inserts have a shape that corresponds to the shape of the seats. Since the cutting inserts are on-edge or tangentially mounted, the chips created during machining flow over the conical portion and the cylindrical portion in the side of the cutting inserts. Thus, the side surface of the cutting inserts may be damaged and affect the abutment of the cutting inserts when they are indexed to a new cutting position.
Since the round cutting inserts of ""087 have their bottom face 59 seated on the seating face 50 of the pocket, they can be rearwardly seated either in the conical seat as shown in FIG. 5 or in a flat surfaces pocket as shown in FIG. 14. Furthermore, the construction of the cutting insert is such that it cannot function as a radially mounted round cutting insert having a positive rake.
Another type of round cutting insert that has a protrusion extending downwardly from a lower surface thereof is disclosed in Japanese Laid Open Patent Publication No. 11-197906. As shown in ""906, the throw-away tip 10 has a protrusion 13 that extends from the rear surface of a disc-like tip 11. The protrusion is provided with flat locking surfaces 15 that join to flat joint surfaces 22 on the attaching tool. Thus, the throw-away tip 10 is prevented from rotation in its pocket.
A disadvantage of the tool of ""906 is that it enables only two indexing positions of the cutting insert. Furthermore, in order to index the cutting insert the fastening screw 30 has to be completely loosened and the cutting insert has to be removed from its pocket so that it could be rotated to a new indexing position.
In Japanese Laid Open Patent Publication No. 2000-52111 there is disclosed a cutting insert having a protrusion that extends from its rear surface. However, the cutting insert of ""111 is connected to its pocket through heat coupling. This means, that the inner diameter of the recess 25 of the insert pocket 23 is slightly smaller than the outer diameter of the protrusion 32 of the insert 26. Through heat coupling, convex section 32 of chip 26 is coupled with convex recessed section 25 of chip mounting seat 23, and, at the same time, concave recessed section 25 and side walls 23b and 23c apply pressure between convex section 32 and side wall 29.
A disadvantage of the tool of ""111 is that the necessity to abut the side walls 23b and 23c of the pocket limits the operating range angle that may be achieved with such a tool. Furthermore, the retaining of the cutting insert through heat coupling limits the simple indexing of the cutting insert within its pocket.
It is one object of the present invention to provide a cutting tool and a round cutting insert therefor that significantly reduces or overcomes the aforementioned disadvantages.
It is a further object of the present invention to provide a secure clamping arrangement for securing the cutting insert to the cutting tool.
It is still a further object of the present invention to provide rotation limiting means to enable easy indexing of the cutting insert in its pocket.
In accordance with the present invention there is provided a cutting tool having a longitudinal axis (A), the cutting tool comprises a tool body, having at least one mounting leg formed at a forward portion thereof, the at least one mounting leg comprises an insert receiving pocket and a cutting insert retained therein;
the insert receiving pocket comprising:
a base wall and a side wall transversely directed to the base wall;
a substantially circular recess extending downwardly from the base wall, the recess having a lower wall bounded by an upstanding peripheral wall, and
a threaded bore having a threaded bore axis (B) and extending downwardly from the lower wall of the recess;
the cutting insert comprising:
an upper surface, a lower surface and a side surface extending between the upper surface and the lower surface,
continuously peripherally extending cutting edge portions defined at an intersection between the upper surface and the side surface;
a cylindrical protrusion extending downwardly from the lower surface, the cylindrical protrusion having a bottom surface surrounded by a peripheral surface, and
a through bore having a bore axis (E) and extending between the upper surface and the bottom surface;
wherein:
a retaining screw passes through the through bore and threadingly engages the threaded bore;
the peripheral surface of the cutting insert abuts the peripheral wall of insert receiving pocket; and
the lower surface of the cutting insert abuts the base wall of the insert receiving pocket.
If desired, the cutting insert subtends an operating range angle (xcex4) of 330xc2x0 at the bore axis (E).
Preferably, the upstanding peripheral wall is provided with a cutout that extends axially rearwardly and radially inwardly with respect to the longitudinal axis.
Typically, the cutout subtends a relief angle (xcex1) at the axis of the threaded bore (B) in the range from 30xc2x0 to 60xc2x0.
According to a specific embodiment of the present invention, the relief angle (xcex1) is 40xc2x0.
Preferably, the peripheral surface abuts the peripheral wall along two spaced apart contact regions adjacent the cutout.
Preferably, the side wall comprises rotation limiting means, wherein the side surface comprises rotation limiting surfaces and wherein the rotation limiting surfaces are adapted to abut the rotation limiting means.
Preferably, the cutting edge portions define a continuously peripherally extending round cutting edge.
Typically, the rotation limiting means is a flexible member.
Further typically, the rotation limiting means is an outwardly urged plunger.
Still further typically, the plunger is urged outwardly by means of a spring.
According to as specific embodiment of the present invention, the plunger is a ball plunger.
Typically, the rotation limiting surfaces are indexing abutment surfaces adapted to abut the plunger.
According to a specific embodiment of the present invention, the indexing abutment surfaces of the cutting insert are flat.
According to a preferred embodiment of the present invention, the indexing abutment surfaces of the cutting insert are indented.
Typically, the cutting insert has at least three indexing abutment surfaces.
Preferably, the rotation limiting means abuts a single rotation limiting surface that constitutes an operative rotation limiting surface and wherein the side surface remains unabutted except for the operative rotation limiting surface.
Typically, the rotation limiting surfaces are located at the side surface adjacent the lower surface.
According to a preferred embodiment, the rotation limiting surfaces are located at the side surface and open to the lower surface.
Preferably, the plunger forms an internal acute angle (xcex2) with the axis (B) of the threaded bore.
Typically, the internal acute angle (xcex2) is in the range from 70xc2x0 to 80xc2x0.
According to a specific embodiment of the present invention, the internal acute angle (xcex2) is 73xc2x0.
Preferably, the recess has a first diameter (D1), the protrusion has a second diameter (D2) and wherein the first diameter is larger than the second diameter.
Typically, the first diameter (D1) is larger than the second diameter (D2) by 0.01 mm to 0.03 mm.
Preferably, the upstanding peripheral wall is perpendicular to the base wall.
Further preferably, the peripheral surface is perpendicular to the lower surface.
Still further preferably, the axis (B) of the threaded bore is parallel to the axis (E) of the bore and spaced apart therefrom a first distance (L) and wherein the axis of the threaded bore is closer to the cutout than the axis of the bore.
Generally, when the protrusion is within the recess without the retaining screw threadingly engaging the threaded bore the rotation limiting means assists in adjusting the axis of the bore to be parallel to the axis of the threaded bore.
Further generally, when the protrusion is within the recess without the retaining screw threadingly engaging the threaded bore the rotation limiting means prevents falling of the cutting insert out of the insert receiving pocket.
Preferably, the rotation limiting surfaces are equally peripherally spaced around the side surface and form a plurality of indexing positions wherein when the protrusion is within the recess without the retaining screw threadingly engaging the threaded bore or when the retaining screw partially engages the threaded bore the cutting insert can be rotated around the axis of the bore from one indexing position to another indexing position.
Typically, a mechanical signal is provided when the cutting insert is indexed from one indexing position to another indexing position.
Generally, resistance to rotation of the cutting insert produces the mechanical signal.
If desired, the mechanical signal is a click.
Further if desired, the indexing positions are marked at the upper surface by indexing numerals.
There is also provided in accordance with the present invention a cutting insert, comprising:
an upper surface, a lower surface and a side surface extending between the upper surface and the lower surface,
continuously peripherally extending cutting edge portions defined at an intersection between the upper surface and the side surface;
a cylindrical protrusion extending downwardly from the lower surface, the cylindrical protrusion having a bottom surface surrounded by a peripheral surface, and
a through bore having a bore axis (E) and extending between the upper surface and the bottom surface;
wherein:
the side surface comprises rotation limiting surfaces adjacent, and open to, the lower surface.
Preferably, the cutting edge portions define a continuously peripherally extending round cutting edge.
Generally, the rotation limiting surfaces are indexing abutment surfaces.
According to a specific embodiment of the present invention, the indexing abutment surfaces are flat.
According to a preferred embodiment of the present invention, the indexing abutment surfaces are indented.
Typically, the cutting insert has at least three indexing abutment surfaces.
Preferably, the peripheral surface is perpendicular to the lower surface.
Further preferably, the rotation limiting surfaces are equally peripherally spaced around the side surface and form a plurality of indexing positions.
If desired, the indexing positions are marked at the upper surface by indexing numerals.